Electrical resistance change method has been applied to monitor a delamination crack of
a thin CFRP laminate. For a thick CFRP laminate, multiple delamination cracks are made with
many matrix cracks, and the electric current in the thick CFRP laminate may not flow in the
thickness direction due to the strong orthotropic electrical conductivity. The present study employs
an electric impedance change method for the identification of damage location and dimension of the
damaged area; applicability of the method is investigated experimentally using thick beam-type
specimens fabricated from cross-ply laminates of 36 plies. After making the damage, electrical
impedance was decreased. A residual stress relief model was proposed to explain the decrease.
From the measured electrical impedance changes, the relationships between the electrical
impedance changes and damages are obtained by means of response surfaces. The response surfaces
estimated the damage location and dimension of the damaged area exactly even for the thick CFRP
laminates. The electrical impedance change method can be used as an appropriate sensor for
measurement of residual stress relief due to damages of thick CFRP laminates.